U.S. Pat. No. 6,843,613 to Gelfand, et al. discloses an energy absorbing system forming part of an automobile barrier for placement preferably at a railroad crossing. The system includes a net stored in a pit spanning a roadway and parallel to railroad tracks. The net may be raised as an automobile approaches along the roadway in a particular travel direction; should the automobile not stop timely it will collide with the net, causing the automobile to cease travel prior to reaching the tracks.
The system of the Gelfand patent also contemplates placing a second automobile barrier opposite the railroad tracks from the first barrier. Such a two-barrier system is depicted especially in FIGS. 1A-1B of the Gelfand patent, with one net impeding automobile travel in a first direction along the roadway and the other net impeding travel in the direction opposite the first direction. In this sense each barrier of the Gelfand patent is only uni-directional, as the structure used to absorb energy functions only when the net is displaced toward the railroad tracks.
U.S. Pat. No. 6,779,756 to Lopez, owned commonly with this application, describes other systems for arresting aircraft or other vehicles. Designed typically for above-ground installation, these systems include dual arresting tapes provided on spools with brake assemblies positioned within hubs of the spools. The arresting tapes are designed for connection to a cable crossing a runway (or other travel area), with the cable being engaged typically by a tail hook associated with the vehicle to be arrested. For purposes of this application, the entire contents of both the Lopez and Gelfand patents are incorporated herein by this reference.